Suction box cover with a surface which merges with holes therein by concavely formed intermediate surfaces

ABSTRACT

A suction box for a papermaking machine wherein the holes through the suction box cover include, at least the leading and trailing edges thereof, concave edges which prevent wear of the forming wire and prevent rewetting of the paper web.

United States Patent Inventor Alvin C. Roecker Beloit, Wis.

Appl. No. 774,768

Filed Nov. 12, 1968 Patented Nov. 23, 1971 Assignee 'Beloit Corporation Beloit, Wis.

SUCTION BOX COVER WITH A SURFACE WHICH MERGES WITH HOLES THEREIN BY CONCAVELY FORMED INTERMEDIATE SURFACES 2 Claims, 4 Drawing Figs.

US. Cl 162/374, 162/351 Int. Cl D21f l/48 Field of Search 162/374,

[56] References Cited UNITED STATES PATENTS 3,351,524 11/1967 Duncan 162/374 3,352,749 11/1967 Perry 162/354 X 3,052,296 9/1962 Justus 162/374 X 2,682,813 7/1954 Scofield 162/374 3,518,161 6/1970 Ekberg et al 162/374X Primary Examiner-S. Leon Bashore Assistant Examiner-Richard H. Tushin Attorney-Hill, Sherman, Meroni, Gross & Simpson ABSTRACT: A suction box for a papermaking machine wherein the holes through the suction box cover include, at least the leading and trailing edges thereof, concave edges which prevent wear of the forming wire and prevent rewetting ofthe paper web.

SUCTION BOX COVER WITH A SURFACE WHICH MERGES .WITH HOLES THEREIN BY CONCAVELY FORMED INTERMEDIATE SURFACES BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to suction boxes for use in papermaking machines and more particularly, to an improved suction box cover structure for use in papermaking machines such as, Fourdrinier machines.

2. Description of the Prior Art In Fourdrinier machines, the suction boxes are employed to assist in the removal of water from the newly formed paper web carried on a traveling forming wire, and in cylinder machines suction boxes are used to assist in the removal of water from the paper web carried on a felt. In either case, a permeable forming band is trained across the suction box top carrying the paper web thereon and suction through the suction box cover is applied to the underside of the permeable band to assist in removal of water from the web through such permeable band. The holes formed in the suction box cover may take several forms, however, such holes are usually found in the form having a rectangular cross section (slots) or round cross section (circular holes).

There have been numerous improvements in suction box covers wherein the shape of curvature of the cover or the angular disposition of the holes with respect to web travel is concerned. However, it has been found that the shape of the holes in a suction box cover, in particular at least at the leading and the trailing edges of such holes, plays an important role in the prevention of wear of the forming surface and in the quality of the product formed thereon.

SUMMARY OF THE INVENTION According to the invention, a suction box cover is formed with a plurality of holes therein, each of the holes having at least the leading and trailing edges thereof formed in such a manner so as to overcome the above-mentioned disadvantages. The circular holes or rectangular slots, as the case may be, for the suction box covers of the present invention have their edges concavely machined at a slight radius. This radius is important in that, while a knife edge will function to increase the removal of water, such an edge is detrimental to the surface carried by the suction box cover and has a tendency to cause marking of the paper carried thereon. In addition, a rounded edge may cause rewetting of the web which, of course, is also an undesirable condition in that it is self-defeating in the purpose of removing water and it lowers the quality of the paper product.

BRIEF DESCRIPTION OF THE DRAWING The invention, its construction and organization, according to some illustrative embodiments thereof, will be best understood from the following description taken in conjunction with the accompanying drawing, in which:

FIG. 1 is a top plan view of a portion of a suction box cover of the type having suction holes of circular cross section according to the present invention.

FIG. 2 is a sectional view of the apparatus of FIG. I taken along the line II-Il;

FIG. 3 is a top plan view of a portion of a suction box cover of the type having suction holes of rectangular cross section according to the invention; and

FIG. 4 is a sectional view of the apparatus of FIG. 3 taken along the line IVIV.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a papermaking machine, for example a Fourdrinier machine, an endless forming wire is trained about a breast roll at one end and a couch roll at the other end to form a continuously moving perforate forming surface for carrying a newly formed web of paper stock fibers which have been transported to the forming surface as a slurry of the stock fibers in water. As the paper web and the forming wire pass over rollers located immediately downstream of the forming point which break the surface tension of the water whereupon the paper web is partially dewatered. Following this partial dewatering function, the web and forming surface pass over the plurality of suction boxes having perforate covers which support the forming wire from beneath while suction is applied thereto through the holes in the suction box covers. The present invention resides in an improved structure for a suction box cover to increase dewatering of the web as shown in FIGS. 1 to 4 of the drawings.

In FIGS. 1 and 2 of the drawings, a portion of a suction box top surface or cover is shown generally at as comprising a sheet 11 through which a plurality of holes 12a, 12b, 12c, etc., extend. Sheet 11 includes an upper surface 13 which is joined to the inner surface which define holes 12 by a concavely fonned surface 14, further referenced 14a, 14b, 140, etc., at the upper surface of sheet 11. This formed surface has a profile which is curved, preferably at a radius of 0.003 to 0.005 inches, to overcome the above-mentioned disadvantages of wearing the perforate carrier and rewetting of the product. A

In FIGS. 3 and 4, a suction box top or cover is shown generally at as comprising a sheet 21 through which extend a plurality of slots 22a, 22b, which are defined by sidewalls 25, 26, 27 and 28 and by end walls of which walls 29 and 30 are shown. The sheet 21 has an upper surface 23 which merges with sidewalls -28 of slots 22a and 22b by way of concavely curved surfaces 24a, 24b, 24c and 24d which are the leading and the trailing edges of the slots.

In the drawings, arrows and 40 denote the direction of web travel, therefore, in the case of the cover illustrated in FIGS. 1 and 2, and the cover illustrated in FIGS. 3 and 4, the formed edges 14 and 24 are disposed on at least the leading and trailing edges of their respective holes and slots.

It was mentioned above that the radius of curvature of the surface 14 and 24 is preferably in the range of from 0.003 to 0.005 inches. In addition, for the case of the circular holes, the preferred vertical departure is preferred to be in the range of from 0.003 to 0.007 inches and the horizontal departure to be in the range of from 0.1 to 0.4 inches, the departure being the amount of horizontal or vertical surface machined away in forming the curved surfaces. For the slotted suction box cover the preferred vertical departure is in the range of from 0.003 to 0.010 inches while the horizontal departure is in the range of from 0.1 to 0.4 inches. In either of these cases the land area between holes or slots in the direction of web travel is in the range of from 0.5 to L0 inches.

While I have described my invention by reference to particular illustrations of embodiments thereof, it is to be understood that changes and modifications may be made in my invention without departing from the spirit and scope thereof as set forth in the appended claims.-

What I claim as may invention is:

1. In a papermaking machine having an endless traveling perforate-forming surface and a suction box beneath said forming surface for the removal of water, a web of paper being formed on the perforate surface, said suction box including an upper surface having a plurality of circular holes therein, the improvement comprising:

a formed edge on at least the leading and-trailing edges of each of said holes whereby the inner defining surface of said holes merges with the upper surface of the suction box through an intermediate surface which is concavely curved with a profile defined by a radius of from 0.003 to 0.005 inches,

the horizontal departure of said edge being in the range of 0.] to 0.4 inches, and

the vertical departure of said formed edge being in the range of from 0.003 to 0.007 inches.

2. In a papermaking machine having an endless traveling perforate-forming surface and a suction box beneath said forming surface for the removal of water in accordance with claim 1 wherein said holes are elongated slots which extend transverse to the direction of web travel and wherein the formed edges on the leading and trailing edges of said slots have a vertical departure in the range of from 0.003 to 0.01 5 inches. 

2. In a papermaking machine having an endless traveling perforate-forming surface and a suction box beneath said forming surface for the removal of water in accordance with claim 1 wherein said holes are elongated slots which extend transverse to the direction of web travel and wherein the formed edges on the leading and trailing edges of said slots have a vertical departure in the range of from 0.003 to 0.01 inches. 